The manner in which protein, phospholipid and pigment components are assembled into functional energy transducing membranes will be investigated in a bacterial model system. Thus far putative transient membrane invagination sites that give rise to the mature intracytoplasmic photosynthetic membrane have been isolated from Rhodopseudomonas sphaeroides and Rhodospirillum rubrum. A satisfactory procedure for the further purification of these membrane sites is under development so that the characterization of this material can be completed. The rates of assembly of polypeptide components of pigment-protein complexes will be elucidated in the various differentiated regions of the membrane. Attempts to demonstrate polypeptide precursors for the apoprotein components of these complexes will be continued in pulse-chase, permeabilized cell and in vivo protein synthesis studies. The in vitro system will be coupled to membrane vesicles from photosynthetically incompetent mutant strains and the restoration of phototrapping activity will provide a unique functional assay for a system coupling translation and insertion of membrane proteins. A detailed functional and structural examination of the pigment and protein components of newly isolated light-harvesting complexes will be continued. Enzymes of phospholipid biosynthesis will be studied to unambiguously localize the sites of chromatophore phospholipid formation. The proposed studies will aid in the elucidation of mechanisms involved in organelle assembly and will provide a more complete understanding of this process at the molecular level.